This method is intended for mounting installations in particular comprising a fluid transport pipe and an in-line structure deployed along the pipe.
An “in-line structure” refers to structures or equipment attached or connected to at least one section of pipe so as to form a secured assembly that is installed together by a placement vessel. The in-line structure is most often connected to the pipe on board the placement vessel and is next deposited in line over the course of mounting of the pipe.
The fluid transport pipe is preferably a rigid pipe made from an assembly of metal tubes and intended for undersea hydrocarbon extraction.
In undersea installations, it is known to deploy, along the pipe, in-line structures including connection or flow rate monitoring functionalities, such as valves, wellheads, T-connections, etc.
These in-line structures are for example pipeline end termination (PLET) or flow line terminal assembly (FTA) structure, for in-line T-connections (ILT for “inline tee”; ITA for “inline tee assembly”).
The in-line structures are sometimes bulky and heavy. Furthermore, in some cases, the ground on which the installation is placed is movable and unstable.
To ensure proper positioning of the installation, it is then necessary to first place a foundation on the bottom of the body of water, then to deposit the in-line structure and the sections of pipe connected to the in-line structure on the foundation using a traditional placement technique, for example J or S or using the so-called reeled pipe technique, well known by those skilled in the art.
In the case of a rigid pipe, the positioning of the in-line structure on the foundation may prove tedious. It is in fact necessary to target the foundation when lowering the in-line structure to ensure that the in-line structure indeed rests on the foundation.
The in-line structure, and the rigid pipe sections connected to the in-line structure, can then be placed without guidance, while being free to move.
Furthermore, uncontrolled movements of the in-line structure can occur during the operation of the field, due to thermal constraints applied to the pipe, which may move it away from the foundation.
Such a solution is often difficult to carry out in practice or creates excess costs for the installation project. Indeed, such placement then requires increasing the dimensions of the foundation to offset the unknowns of the placement.
To offset this problem, permanent guides are installed on the foundation, before positioning the rigid pipe and the in-line structure thereon. These guides define a positioning axis of the rigid pipe on the foundation.
Such a solution is not fully satisfactory, since it requires very precise alignment of the pipe with the positioning axis during placement of the structure, in order to insert the section(s) of pipe in the guides. This considerably complicates the placement operations.
Furthermore, placement may cause new stresses that are applied on the sections of pipe, for example creating twisting that may prove harmful to the lifetime of the pipe.